Portable electronics devices use batteries that require periodic recharging. Conventional recharging techniques include both wired and wireless approaches. In an exemplary wired recharging technique, an electrical power adapter includes an electrical cord and power converter for plugging into the portable device on one end and a power outlet, such as a wall socket, on the other end.
In an exemplary wireless recharging technique, a power supply pad is configured for wireless power transmission. The power supply pad is typically connected to wall socket via a power cord. The power supply pad includes a power transmitter for wireless power transmission to a portable electronics device having a power receiver. The power transmitter includes a communications processing block and a power transmitting element, such as a coiled wire antenna. The power transmitting element generates a magnetic field through which power is wirelessly transmitted. The magnetic field orientation is a function of the transmission frequency and the physical orientation of the power transmitting element. Conventional power supply pads transmit at a constant frequency, and since the physical orientation of the power transmitting element is also fixed, the magnetic field generated by the power transmitting element of the power supply pad has a specific fixed orientation. The portable electronic device, such as a cellular telephone, includes a communications processing block and a power receiving element, such as a coiled wire antenna. To receive power from the power supply pad, the portable electronic device must be positioned within range of the magnetic field generated by the power transmitting element of the power supply pad. For optimized energy transfer, the portable electronic device must also be properly oriented relative to the power transmission element. Due to the specific orientation of the magnetic field generated by the power transmission element, the power receiving element of the portable electronic device must be properly oriented with the magnetic field or else the wireless power transmission is not optimized or can not be completed. This requires meticulous placement of the portable electronic device on or near the power supply pad, which can be time consuming and frustrating for the end user.
In some applications, the power supply pad is fitted with a cradle, or other type of device place holder, sized to receive the portable electronic device in a specific orientation. The cradle is oriented within the power supply pad so that when the portable electronic device is positioned within the cradle, the power receiving element of the portable electronic device is properly aligned with the power transmission element, and therefore the magnetic field, of the power supply pad. However, having to place the portable electronic device within the cradle almost defeats the purpose of a wireless power transmission application designed for free placement of the device without need for a hard connection to a power source.
Conventional power supply pads are also configured to transmit a fixed amount of power. In applications designed to charge a single portable electronic device at a time, the power supply pad is designed and manufactured to transmit a fixed amount for power compatible for the single portable electronic device, for example 5 W. In other applications, the power supply pad is intended for charging multiple devices concurrently. In this case, the power supply pad is designed and manufactured having a much larger fixed power transmission level, for example 15 W or 20 W. This fixed power transmission level is sufficient for peak power transfer to a maximum number of portable electronic devices. However, when fewer than the maximum number of devices are being charged, the power transmission level is excessive. Further, charging multiple devices concurrently suffers from the same orientation related issues as the single device system.